Association of multi-phase rates of force development during an isometric leg press with vertical jump performances.

PURPOSE: This study aimed to elucidate characteristics of explosive force-production capabilities represented by multi-phase rate of force developments (IRFDs) during isometric single-leg press (ISLP) through investigating relationships with countermovement (CMJ) and rebound continuous jump (RJ) performances. METHODS: Two-hundred-and-thirty male athletes performed ISLP, CMJ with an arm swing (CMJAS), and RJ with an arm swing (RJAS). IRFDs were measured during ISLP using a custom-built dynamometer, while CMJAS and RJAS were measured on force platforms. The IRFDs were obtained as rates of increase in force across 50 ms in the interval from the onset to 250 ms. Jump height (JH) was obtained from CMJAS, while RJAS provided JH, contact time (CT), and reactive strength index (RSI) values. RESULTS: All IRFDs were correlated with CMJAS-JH (ρ = 0.20-0.45, p ≤ 0.003), RJAS-JH (ρ = 0.22-0.46, p ≤ 0.001), RJAS-RSI (ρ = 0.29-0.48, p < 0.001) and RJAS-CT (ρ = -0.29 to -0.25, p ≤ 0.025). When an influence of peak force was considered using partial rank correlation analysis, IRFDs during onset to 150 ms were correlated with CMJAS-JH (ρxy/z = 0.19-0.36, p ≤ 0.004), IRFDs during onset to 100 ms were correlated with RJAS-JH and RJAS-RSI (ρxy/z = 0.33-0.36, p < 0.001), and IRFD during onset to 50 ms was only correlated with RJAS-CT (ρxy/z = -0.23, p < 0.001). CONCLUSION: The early phase (onset to 150 ms) IRFDs measured using ISLP enabled the assessment of multiple aspects of leg-extension strength characteristics that differ from maximal strength; these insights might be useful in the assessment of the athletes' leg-extension strength capabilities.

Ascending aortic impedance in young endurance athletes: a time-resolved phase-contrast MRI study.

Ventricular-vascular coupling in endurance athletes remains incompletely understood. The purpose of this study was to determine the ascending aortic impedance in endurance athletes and explore its associations with traditional cardiovascular measurements. In 15 young male endurance runners and 19 young healthy men, time-resolved (CINE) two-dimensional (2-D) phase-contrast MRI quantified the ascending aortic flow while the pressure waveform was simultaneously collected via a generalized transfer function. The aortic impedance modulus and phase were calculated in the frequency domain while characteristic impedance (ZcF) was calculated by averaging moduli between the 4th and 8th heart rate (HR) harmonics. Stroke volume (SV), left ventricular (LV) morphometry, double product, aortic compliance, and total peripheral resistance (TPR) were also measured. Endurance athletes had higher SV, slower HR, greater LV end-diastolic volume and mass, and lower double product than sedentary participants (all P < 0.05). ZcF was significantly lower in athletes than in sedentary participants (73.3 ± 19.2 vs. 93.4 ± 19.0 dyn·s/cm5, P = 0.005). Furthermore, ZcF was negatively correlated with SV (r = -0.691) and aortic compliance (r = -0.601) but was positively correlated with double product (r = 0.445) and TPR (r = 0.458; all P < 0.05). Multivariate analysis revealed that ZcF was the strongest predictor of SV followed by TPR and HR (adjusted R2 = 0.788, P < 0.001). Therefore, our findings collectively suggest that LV afterload quantified by aortic ZcF is significantly lower in endurance athletes than in sedentary adults. The lower pulsatile LV afterload may contribute to greater SV in endurance athletes.NEW & NOTEWORTHY This is the first study to investigate aortic impedance with the noninvasive, simultaneous recordings of aortic pressure using SphygmoCor XCEL and flow using phase-contrast MRI. We found that the characteristic impedance (Zc) is significantly lower in endurance athletes than sedentary adults, is the strongest predictor of stroke volume (SV), and is inversely associated with aortic compliance. These findings suggest that aortic impedance is a key determinant of the ventricular-vascular coupling adapted to long-term training in endurance athletes.

Distal muscle cross-sectional area is correlated with shot put performance.

Shot putters throw a heavy shot by "pushing". Pushing involves the coordinated extension of multiple joints and is a common motor task for both upper and lower limbs. In lower limb musculature, proximal-specific development and association with motor performance have been shown in athletes. However, as the upper limb is not mechanically loaded to support the body during daily locomotion, it may develop differently from the lower limb. We investigated the cross-sectional area of the prime movers of the upper limb and upper trunk (pectoralis major, deltoid, triceps brachii, and palmar flexors) in eleven male shot put athletes and fourteen untrained males by obtaining magnetic resonance images and manually tracing the muscles on the images. All target muscles were significantly larger in athletes than non-athletes (p < 0.01), with "huge" effect sizes for the pectoralis major and palmar flexors (d = 2.74, 2.04). All target muscle cross-sectional areas were positively correlated with season best record (r ≥ 0.62, p ≤ 0.04), with a particularly strong correlation for the palmar flexors (r = 0.96). These results suggest that the distal muscles of the upper limb are also expected to develop and are strongly associated with motor performance. This is especially true for the distal upper limb muscles (palmar flexors) in shot putters. These findings provide insight into potential training interventions for athletic performance in forceful upper limb movements.

Microstructural organization of the corpus callosum in young endurance athletes: A global tractography study.

Introduction: Aerobic exercise training has been shown to improve microstructural organization of the corpus callosum (CC); however, evidence of this topographic effect is limited. Purpose: To compare the CC microstructural organization between endurance athletes and sedentary adults using a white-matter fiber tractography approach. Materials and methods: Diffusion tensor imaging (DTI) and T1-weighted structural data were collected from 15 male young endurance athletes and 16 age- and sex-matched sedentary adults. DTI data were analyzed with a global probabilistic tractography method based on neighborhood anatomical information. Fractional anisotropy (FA) and mean, radial (RD), and axial diffusivities were measured in the eight CC tracts: rostrum, genu, splenium, and body's prefrontal, premotor, central, parietal, and temporal tracts. Cortical thickness of the CC tract endpoints and the CC tract length and volume were also measured. Physical activity level was assessed by metabolic equivalents (METs). Results: The athlete group had an average VO2max of 69.5 ± 3.1 ml/kg/min, which is above 90%ile according to the American College of Sports Medicine guideline. Compared with the sedentary group, the athlete group had higher FA in the CC body's premotor and parietal tracts and the CC splenium. These tracts showed lower RD in the athlete compared with sedentary group. The voxelwise analysis confirmed that the athlete group had higher FA in the CC and other white matter regions than the sedentary group, including the corona radiata, internal capsule, and superior longitudinal fasciculus. Cortical thickness of the CC tract endpoints and the CC tract lengths and volumes were similar between the two groups. Physical activity levels were positively correlated with FA in the CC body's parietal (r = 0.486, p = 0.006) and temporal (r = 0.425, p = 0.017) tracts and the CC splenium (r = 0.408, p = 0.023). Conclusion: Young endurance athletes have higher microstructural organization of the CC tracts connected the sensorimotor and visual cortices than the age- and sex-matched sedentary adults.

Long-term effects of school barefoot running program on sprinting biomechanics in children: A case-control study.

BACKGROUND: The acute changes of running biomechanics in habitually shod children when running barefoot have been demonstrated. However, the long-term effects of barefoot running on sprinting biomechanics in children is not well understood. RESEARCH QUESTION: How does four years of participation in a daily school barefoot running program influence sprint biomechanics and stretch-shortening cycle jump ability in children? METHODS: One hundred and one children from barefoot education school (age, 11.2 ±â€¯0.7 years-old) and 93 children from a control school (age, 11.1 ±â€¯0.7 years-old) performed 50 m maximal shod and barefoot sprints and counter movement jump and five repeated-rebound jumping. To analyse sprint kinematics, a high-speed camera (240 fps) was used. In addition, foot strike patterns were evaluated by using three high-speed cameras (300 fps). Jump heights for both jump types and the contact times for the rebound jump were measured using a contact mat system. Two-way mixed ANOVA was used to examine the effect of school factor (barefoot education school vs control school) and footwear factor (barefoot vs shod) on the sprinting biomechanics. RESULTS: Sprinting biomechanics in barefoot education school children was characterised by significantly shorter contact times (p = 0.003) and longer flight times (p = 0.005) compared to control school children regardless of footwear condition. In shod sprinting, a greater proportion of barefoot education school children sprinted with a fore-foot or mid-foot strike compared to control school children (p < 0.001). Barefoot education school children also had a significantly higher rebound jump height (p = 0.002) and shorter contact time than control school children (p = 0.001). SIGNIFICANCE: The results suggest that school-based barefoot running programs may improve aspects of sprint biomechanics and develop the fast stretch-shortening cycle ability in children. In order to confirm this viewpoint, adequately powered randomised controlled trials should be conducted.

Proximal Aortic Compliance in Young Male Endurance Athletes: An MRI Study.

INTRODUCTION: High-intensity endurance training can elicit profound cardiac adaptations; however, the current evidence as to its impact on the proximal aorta is limited. The purpose of this study was to investigate the morphological and functional characteristics of the proximal aorta in endurance athletes. METHODS: Fifteen young male middle- and long-distance runners were compared with 19 age- and sex-matched sedentary control participants. CINE phase-contrast magnetic resonance imaging was used to measure blood flow velocities and cross-sectional areas of the ascending and proximal descending aorta. Aortic blood pressure was measured simultaneously during the phase-contrast magnetic resonance imaging scan using a generalized transfer function. Maximal oxygen uptake (V˙O2max) was measured in the athletes. Left ventricular morphology was assessed in a subgroup of participants (n = 16) with cardiac magnetic resonance imaging. RESULTS: The athlete group exhibited an average V˙O2max of 69.5 ± 3.1 mL·kg-1⋅min-1, which is above the 90th percentile of men with similar age according to the American College of Sports Medicine guideline. The athletes had significantly higher stroke volume and slower heart rate at rest and greater left ventricular end-diastolic volume and mass than the sedentary participants. Significantly larger cross-sectional areas and higher compliance of the ascending and proximal descending aorta were also found in the athletes, independently of body surface area. Moreover, higher compliance of the ascending aorta was associated with greater stroke volume (r = 0.382, P = 0.026) and slower heart rate (r = -0.442, P = 0.009) across all participants. CONCLUSIONS: The proximal aorta of young male endurance athletes undergoes morphological and functional adaptations that may be resulting from the significant hemodynamic alterations associated with their cardiac function.

Effects of Joint Kinetics on Energy Cost during Repeated Vertical Jumping.

PURPOSE: The present study was designed to investigate the effects of lower limb joint kinetics on energy cost during jumping. METHODS: Eight male middle and long-distance runners volunteered for the study. The subjects were asked to repeat vertical jumps at a frequency of 2 Hz for 3 min on a force platform in three different surface inclination conditions: Incline (+8°), Level (0°), and Decline (-8°). Sagittal plane kinematics were obtained using a high-speed video camera. Simultaneously, ground reaction forces and EMG of the lower limb muscles were recorded. Energy cost was calculated using steady-state oxygen uptake, respiratory ratio, and vertical distance of the body. RESULTS: In all conditions, energy cost correlated positively with total mechanical work of the knee joint (r = 0.636, P < 0.01), but negatively with total mechanical work of the ankle joint (r = -0.584, P < 0.01). The muscle-tendon complex length of the gastrocnemius and soleus muscles were significantly longer in incline than in level and decline. The gastrocnemius muscle showed different activity pattern in decline as compared with the incline and level conditions. CONCLUSIONS: The present study revealed that the ankle and knee joint kinematics and, therefore muscles' coordination are associated with energy cost during repeated vertical jumping. The lower limb joints contributed different efficiencies to generate the same total mechanical work in repeated vertical jumping on different surface inclinations. Energy cost was smaller when mechanical work was mainly done by ankle joint. Whereas, when the ankle joint did less mechanical work, the knee and/or hip joints compensated for the lack of mechanical work of the ankle joint and energy cost was increased.

Kinematic characteristics of barefoot sprinting in habitually shod children.

BACKGROUND: Anecdotally, a wide variety of benefits of barefoot running have been advocated by numerous individuals. The influence of the alterations in the properties of the shoe on the running movement has been demonstrated in adults at submaximal jogging speeds. However, the biomechanical differences between shod and barefoot running in children at sprinting speeds and the potential developmental implications of these differences are still less examined. The purpose was to determine the potential differences in habitually shod children's sprint kinematics between shod and barefoot conditions. METHODS: Ninety-four children (51 boys and 43 girls; 6-12 years-old; height, 135.0 ± 0.12 m; body mass, 29.0 ± 6.9 kg) performed 30 m maximal sprints from standing position for each of two conditions (shod and barefoot). To analyze sprint kinematics within sagittal plane sprint kinematics, a high-speed camera (300 fps) was set perpendicular to the runway. In addition, sagittal foot landing and take-off images were recorded for multiple angles by using five high-speed cameras (300 fps). Spatio-temporal variables, the kinematics of the right leg (support leg) and the left leg (recovery leg), and foot strike patterns: rear-foot strike (RFS), mid-foot strike (MFS), and fore-foot strike (FFS) were investigated. The paired t-test was used to test difference between shod and barefoot condition. RESULTS: Barefoot sprinting in habitually shod children was mainly characterized by significantly lower sprint speed, higher step frequency, shorter step length and stance time. In shod running, 82% of children showed RFS, whereas it decreased to 29% in barefoot condition. The touch down state and the subsequent joint movements of both support and recovery legs during stance phase were significantly altered when running in condition with barefoot. DISCUSSION: The acute effects of barefoot sprinting was demonstrated by significantly slower sprinting speeds that appear to reflect changes in a variety of spatiotemporal parameters as well as lower limb kinematics. It is currently unknown whether such differences would be observed in children who typically run in bare feet and what developmental benefits and risks may emerge from increasing the proportion of barefoot running and sprinting in children. Future research should therefore investigate potential benefits that barefoot sprinting may have on the development of key physical fitness such as nerve conduction velocity, muscular speed, power, and sprinting technique and on ways to minimize the risk of any acute or chronic injuries associated with this activity.

Evaluation of pulse height control for rapid isometric contractions in college sprinters.

The ability of rapid force development is one of the important factors for improving physical performance. It has been known that rapid isometric force is controlled by a central motor program to maintain the rise time relatively constant independent of force amplitude (pulse height control). The advantage of using pulse height control is that it increases the rate of force with force amplitude. However, this strategy is believed to be applicable up to about 50-60% of maximal voluntary contractions (MVC). When the force level increases further, individuals often switch to pulse width control to increase the time to peak force. The aim of this study was to determine the force level (turning point) at which participants switch from pulse height control to pulse width control. This turning point was defined as the maximum force produced by pulse height control. We then attempted to examine whether this turning point is different among participants (control and sprinter groups). Therefore, participants were asked to perform isometric plantar flexions as fast as possible over a wide range of force levels (10-90%MVC). Our results showed that a turning point (%MVC) between two strategies was detected in all participants and the mean values were significantly higher in the sprinter group than that in the control group. Our results suggest that each participant has different limits of force level produced by pulse height control. The sprinter and control groups may use different control strategies for rapid force production at a higher force level.